Fuel control system

ABSTRACT

An internal combustion engine 30 capable of operating on petrol an/or methanol has an adaptive control system responsive to a lambda-sensor (23), a limiter device (21) and a multiplier device (22) which, in response to the richness of the air/fuel mixture, produce a signal (FMCOR) for influencing the fuel injection times (t i ).

FIELD OF THE INVENTION

The present invention relates to an arrangement for and a method ofdetecting the amount of one constituent in a mixture of fuelconstituents.

BACKGROUND OF THE INVENTION

The number of internal combustion engines is growing in whichalternative fuels or a mixture of fuels can be used. The advantages ofsuch arrangements are discussed, for example, in DE-A-2544444 and U.S.Pat. No. 4,495,930.

In DE-A-2544444 use is made of the fact that an alcohol/petrol mixturehas an electrical conductivity which varies in dependence on the ratioof the constituents. The fuel/air ratio required for optimal operationalso varies with the fuel constituents and so the opening time of thefuel supply means is varied in dependence on the conductivitymeasurement. A disadvantage of this arrangement is that an extracomponent i.e. a sensor is required to measure the conductivity; thisadds weight and expense.

SUMMARY OF THE INVENTION

The present invention seeks to provide an improved solution.

According to a first aspect of the present invention there is providedan internal combustion engine capable of operating on first and secondkinds of fuel or a mixture thereof characterised in that there isprovided sensor means for producing a signal representative of therichness of the air/fuel mixture, and means for processing said signalto influence an operating parameter of the engine.

The sensor means is preferably a lambda-probe such as an oxygen sensorin the exhaust of a vehicle engine, and the fuels are methanol andpetrol.

An advantage of this arrangement is that the sensor means is alreadypresent and the added expense, weight and size of a dedicated methanolsensor are avoided.

In a preferred arrangement the processing means produces a feedbacksignal in a loop to provide an adaptive system for controlling theair/fuel supply ratio, that is by controlling the fuel injection times.

The vehicle may be arranged to operate on pure petrol or pure methanolor a mixture of the two.

According to a second aspect of the invention there is provided a methodof determining the amount of one fuel in a mixture in an internalcombustion engine characterised in that said amount is determined from avalue representative of the richness of the fuel mixture.

The present invention is based on the recognition that the controldeviation of a lambda-sensor becomes greater as the methanol fraction inthe supplied fuel mixture increases. The lambda probe output signal ispreferably detected and processed by an engine management system orelectronic control unit with adaptive lambda control, that is aMOTRONIC-control device. The methanol content is calculated from thecontrol deviation and stored in a permanently powered random accessmemory. Thus after switching off the engine and subsequently starting itagain, the stored methanol content value is immediately available.

BRIEF DESCRIPTION OF THE DRAWING

A preferred embodiment of the present invention will now be described,by way of example only, with reference to the accompanying drawing whichshows a lambda closed loop control circuit with pilot controls.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

A MOTRONIC control circuit comprises a plurality of functional blocks 11to 17. Block 11 calculates a fuel injection time t_(E) which is theproduct of engine load t_(L) and a correction factor Fges which takesinto account warm-up, post-start enrichment, intake air temperaturecorrection, acceleration enrichment and the factor from the lambda-map.Thus block 11 receives as inputs signals representative of engine speed,engine load, engine temperature and air temperature.

Block 12 produces a time correction factor to compensate for the factthat the time required for the injection valve to open and to closefully is dependent on the voltage supply. Thus block 12 receives at itsinput a battery voltage signal.

The lambda closed loop control comprises a lambda-sensor 23, that is, anoxygen sensor, and a PI-controller, block 13, with proportional andintegral terms and producing an output factor Fr.

The adaptive pilot control for the lambda closed loop control comprisesblocks 14 to 17. Block 14 is a long time low-pass-filter providing anoutput representing average fuel richness.

I, II and III are the selected ranges for the adaptive pilot control.Block 15 is the adaptive correction for air which is not measured,caused by leakage in the intake manifold. It is used to produce aparameter TRA which is stored in the CMOS RAM in which the acquiredinformation is held until the control device or the battery isdisconnected. N is the engine speed and NO is a reference engine speedvalue, for example, 2000 rpm.

Block 16 is the adaptive correction for the injection valve and producesan output TDTV which is also stored in the RAM. Block 17 is anintegrator for the adaptive correction for the altitude error and forthe correction for the fuel quality, and provides an output FRA, whichis also stored in the RAM. A hot wire air mass meter or other device formeasuring air mass with respect to time may be used to eliminate anyaltitude error. As described so far, the arrangement corresponds to theexisting MOTRONIC control as shown, for example, in FIG. 3 of U.S. Pat.No. 4,440,131.

In the present arrangement, further blocks 21, 22 are provided whichconstitute a flexible fuel adaptation and are an extension of FRAintegrator 17. The range of the output of integrator 17 with petrolalone is 0.8 to 1.2. With flexible fuel, that is, the petrol/methanolalternative a range of 0.8 to 2.0 is required. Block 21 limitsintegrator 17. If FRA reaches the upper limit, block 22 multiplies FMCORby the value of FRA and FRA is then reset. So if the maximum is reached,FRA is reset to 1 and FMCOR new is equal to 1.2 times FMCOR old. Acorresponding procedure is performed at the lower limits of FRA. FMCORis also stored in the RAM.

In normal operation, for example, without any air leakage or altitudeerror, the pilot control is adjusted to the stoichiometric air/fuelratio. The process for achieving this ratio upon a change of fuel isexemplified below.

If at any time there is a step-transition from pure petrol to puremethanol the reset procedure occurs three times in succession. Afterthat the theoretical value of FMCOR is 1.728 (=1.2³) but FMCOR islimited to 2. The remaining control deviation is corrected by FRA. (Inthis example: FRA=1.157). Changing from pure methanol to pure petrol,the corresponding procedure is performed downwards (FMCOR 1). In bothcases FRA can be used for corrections in a range about ±20%, when FMCORhas been adapted.

Then the amount of methanol is calculated by the relation

    Methanol content (in percent)=100*(FMCOR*FRA-1).

This value is used for the appropriate selection of spark timing and forthe selection of different control parameters of the lambda closed loopcontrol which may be affected by a variable methanol content in the fuelmixture.

Blocks 21, 22 may be provided as an optional module so thatlambda-closed loop control alone may be provided or may be combined withthe flexible fuel module. Alternatively the described arrangement can berealized by a different FRA-gauge, i.e. an extended range of theFRA-integrator 17 so there is no need for an additional factor FMCOR.With this alternative, an existing algorithm forlambda-closed-loop-control is affected by different changes. Thus thedescribed embodiment has the additional factor FMCOR as a modularextension of existing and approved softwater.

The corrected fuel injection time signal t_(e) modified by outputs TRA,TDTV and TVUB, is supplied as an actual signal t_(i) to engine 30.

The RAM is a part of the control unit and the engine CPU uses it as anon volatile memory, so power must always be supplied. The RAM issupplied with information during operation of the vehicle dependent uponthe different influences as outlined above. After the engine is switchedoff and is subsequently started again, the adaptive methanol content isimmediately available.

An arrangement in accordance with the present invention can be used in afuel supply system in which there are separate tanks for the differentfuels, for example, as discussed in U.S. Pat. No. 4,495,930 in which theratio between the two kinds of fuel is varied in response to engineload. The deduction of methanol content from the richness of theair/fuel mixture can be used in a feedback loop to check that thecorrect amount of methanol is being supplied to the engine. Means may beconnected to blocks 21, 22 for actually measuring and/or indicating theproportion of methanol in the fuel.

We claim:
 1. An internal combustion engine capable of operating ondifferent kinds of fuel, the engine comprising:sensor means forproducing a signal representative of the richness of the air/fuelmixture; processing means for processing said signal to influence anoperating parameter of the engine; and, said processing means includes alimiter device and a multiplier device.
 2. The engine of claim 1,comprising: a loop for providing an adaptive system for controlling theair/fuel supply ratio; and, said processing means producing a feedbacksignal (FMCOR) in said loop.
 3. The engine of claim 2, wherein saidprocessing means controls the fuel injection times of the engine.
 4. Theengine of claim 1, wherein the fuel has a methanol content, the enginefurther comprising: means for calculating the methanol content of thefuel; and, means for controlling the spark timing in dependence on thecalculated methanol content.
 5. The engine of claim 1, wherein saidsensor means includes a lambda probe arranged in the exhaust of theengine.
 6. The engine of claim 1, wherein the different kinds of fuelinclude a fuel selected from methanol, petrol and a mixture of methanoland petrol.
 7. The engine of claim 1, wherein said limiter device andthe multiplier device are connected to the output of an integrator foradaptive correction.
 8. The engine of claim 7, wherein the output of thelimiter device is fed back to said integrator for resetting saidintegrator.
 9. A control arrangement for an internal combustion enginecapable of operating on different kinds of fuel, the control arrangementcomprising:sensor means for producing a signal representative of therichness of the air/fuel mixture; processing means for processing saidsignal to influence an operating parameter of the engine; and, saidprocessing means including limiter means and multiplier means.
 10. Thecontrol arrangement of claim 9, wherein the different kinds of fuelinclude a fuel selected from methanol, petrol and a mixture of methanoland petrol.
 11. The control arrangement of claim 9, further comprising:a loop for providing an adaptive system for controlling the air/fuelsupply ratio; and, said processing means producing a feedback signal(FMCOR) in said loop.
 12. The control arrangement of claim 11, whereinsaid processing means controls the fuel injection times of the engine.13. The control arrangement of claim 11, further comprising: means forcalculating the methanol content of the fuel; and, means for controllingthe spark timing in dependence on the calculated methanol content. 14.The control arrangement of claim 9, wherein said sensor means includes alambda probe arranged in the exhaust of the engine.
 15. The controlarrangement of claim 9, wherein said limiter means and said multipliermeans are connected to the output of an integrator for adaptivecorrection.
 16. The control arrangement of claim 15, wherein the outputof said limiter means is fed back to said integrator for resetting saidintegrator.